Late delivery of exotic chromium to the crust of Mars by water-rich carbonaceous asteroids
Ke Zhu, Martin Schiller, Lu Pan, Nikitha Susan Saji, Kirsten Larsen, Elsa Amsellem, Courtney Rundhaug, Paolo A. Sossi, I. Leya, Frédéric Moynier, Martin Bizzarro
Abstract
The terrestrial planets endured a phase of bombardment following their accretion, but the nature of this late accreted material is debated, preventing a full understanding of the origin of inner solar system volatiles. We report the discovery of nucleosynthetic chromium isotope variability (μ 54 Cr) in Martian meteorites that represent mantle-derived magmas intruded in the Martian crust. The μ 54 Cr variability, ranging from −33.1 ± 5.4 to +6.8 ± 1.5 parts per million, correlates with magma chemistry such that samples having assimilated crustal material define a positive μ 54 Cr endmember. This compositional endmember represents the primordial crust modified by impacting outer solar system bodies of carbonaceous composition. Late delivery of this volatile-rich material to Mars provided an exotic water inventory corresponding to a global water layer >300 meters deep, in addition to the primordial water reservoir from mantle outgassing. This carbonaceous material may also have delivered a source of biologically relevant molecules to early Mars.